Chlorinated elastomers, such as chlorinated polyethylene, may be cured via various means including the use of peroxide/coagent systems, thiadiazole-based systems, or irradiation crosslinking techniques. Peroxide cures are typically preferred for their scorch safety, shelf-life or bin stability, low permanent set, and high temperature performance. However, peroxide cure systems are often unacceptable for use in molded goods because of mold sticking, and fouling due to volatiles or in applications that require a low temperature cure due to equipment or processing limitations.
Thiadiazole-based cure systems provide certain advantages such as the ability to cure over a wider range of temperature and pressure conditions than peroxide cures while generating fewer volatile byproducts, having good mold release characteristics, and the ability to use less expensive compounding ingredients such as aromatic oils.
U.S. Pat. No. 4,128,510 discloses vulcanizing halogen-containing polymers. The halogen-containing polymers can be crosslinked by heating with certain derivatives of 2,5-dimercapto-1,3,4-thiadiazole, such as the monobenzoate derivative, and a basic material to produce useful vulcanizates of increased strength and insolubility in organic solvents. Concentrates of the derivatives of 2,5-dimercapto-1,3,4-thiadiazole are prepared by incorporating the thiadiazole in a binder material such as a polymer, wax, rosin, etc. for subsequent compounding with the halogen-containing polymer to be crosslinked.
U.S. Pat. No. 4,288,576 discloses 2,5-Dimercapto-1,3,4-thiadiazole as a cross-linker for saturated, halogen-containing polymers. The saturated, halogen-containing polymers are cross-linked to yield stable vulcanizates with good aging, compression set resistance, and insolubility in organic solvents using 2,5-dimercapto-1,3,4-thiadiazole, or a concentrate thereof in a binder material, in the presence of certain basic materials in normal vulcanization procedures.
U.S. Pat. No. 4,482,681 discloses crosslinking halogen-containing polymers. Halogen-containing polymers are crosslinked by heat-curing with a crosslinking system made up of a crosslinking agent, which is either a polymercaptan or an ester derivative thereof, a basic material and a hydrated salt.
U.S. Pat. No. 4,551,505 discloses a process for crosslinking chlorinated polyethylene. The crosslinking of chlorinated polyethylene with 2,5-dimercapto-1,3,4-thiadiazole in the presence of a basic substance is carried out to improve vulcanizate properties.
U.S. Pat. No. 4,745,147 discloses a vulcanizable chlorinated polyethylene composition. The composition includes chlorinated polyethylene containing from 20 to 50 weight percent chlorine, from 0.75 to 3 parts per 100 parts by weight chlorinated polyethylene of a polymercapto compound such as 2,5-dimercapto-1,3,4-thiadiazole, from 0.5 to 20 parts by weight per 100 parts by weight chlorinated polyethylene of an acid acceptor such as magnesium oxide, from 0.25 to 10 parts by weight per 100 parts chlorinated polyethylene of a polyhydric alcohol. Preferably, the composition contains an initiator, which is an amine, quaternary ammonium compound, or a phosphonium compound.
U.S. Pat. No. 5,655,830 discloses a process for controlling premature curing of vulcanizable halogen-containing polymers. The process includes blending before storage, into the vulcanizable composition, a thioester derivative of 2,5-dimercapto-1,3,4-thiadiazole crosslinking agent and polyethylene glycol, whereby the scorch time of the vulcanizable compound is not significantly affected by the water content of the composition.
U.S. Pat. No. 5,686,537 discloses a process for controlling premature curing of vulcanizable halogen-containing polymers.
U.S. Pat. No. 4,591,617 discloses crosslinking compositions for butyl rubber or halobutyl rubber, and epihalohydrin rubber blends. The crosslinking compositions include both sulfur and non-sulfur curative systems, which are particularly adapted for crosslinking rubber blends of (a) from 35 percent to 85 percent halobutyl rubber or a mixture of butyl rubber and halobutyl rubber wherein the halobutyl rubber is at least 50 percent by weight of the mixture, and (b) from 15 percent to 65 percent of an epihalohydrin rubber, and to the rubber materials crosslinked therewith.
U.S. Pat. No. 4,357,446 discloses a curable composition of halogen-containing polymer. The curable composition of a halogen-containing polymer is composed of (1) 100 parts by weight of a halogen-containing polymer, (2) as a crosslinking agent, from 0.1 to 10 parts by weight of a 2,3-dimercapto-pyrazine or -quinoxaline compound having a certain formula, and (3) as an acid acceptor, from 0.5 to 50 parts by weight of a compound of a metal.
U.S. Pat. No. 4,434,274 discloses vulcanizable compositions of halogen and carboxyl containing acrylate elastomers, 2,5-dimercapto-1,3,4-thiadiazole, a Group IVA metal oxide or salt, and a tetraalkyl thiuram sulfide. Dual cure site acrylate elastomers containing both active halogen and carboxyl groups are compounded with a combination of 2,5-dimercapto-1,3,4-thiadiazole, a Group IVA metal oxide or salt thereof, and a tetraalkyl thiuram sulfide to provide compounds having an excellent scorch/cure rate balance, and balance of desirable physical properties in the vulcanizates thereof.
Despite the research efforts in developing and improving the cure rate of chlorinated polyethylenes while maintaining stability at storage temperatures thereof, there is still a need for further improvement in cure rate of chlorinated polyethylenes while maintaining stability at storage and processing temperatures.